While Los Angeles currently ranks third in AIDS cases among U.S. cities, few cases are linked to intravenous drug use (IVDU). Of the 3459 AIDS cases reported as of July 31, 1987, 93% were homosexual or bisexual men and only 89 cases (2.6%) were reported where IV drugs use was the sole risk factor. The proposed project is a 4-year longitudinal study tracing the course of human immunodeficiency virus (HIV) infection in 450 intravenous drug users in Los Angeles County. The study will relate individual characteristics and behaviors to the development of seropositive status and assess the likelihood of diffusion to heterosexual IVDUs. Four groups of narcotics IVDUs will be assessed: men and women subdivided by those with and those without a self-reported history of homosexual experiences in the past 8 years. The specific aims of this project include the annual monitoring over 3 years of (1) rate of change and diffusion of HIV infection in the 4 specified subpopulations; (2) HIV antibody seroprevalence and seroconversion among whites, blacks, and Mexican Americans; (3) to determine knowledge about and attitudes toward AIDS, and level of exposure to education and prevention efforts among the groups studied; (4) to assess self-reported behaviors linked to AIDS transmission; (5) to distinguish between the seropositive and seropositive groups by demographic background, AIDS-related knowledge, attitudes, and risk behaviors; (6) to evaluate the effectiveness of AIDS education and prevention programs; (7) to determine which behaviors predispose an IVDU to continue high risk behaviors despite education and intervention efforts; (8) to monitor the natural history and ARC and AIDS among HIV infected individuals; (9) to gather information useful for the subpopulations studied in planning for prevention, health care, and medical service resource needs. A semi-structured interview will obtain demographic information, drug and sexual histories, and frequency of high risk behaviors, as well as open ended responses to other AIDS-related questions. Analyses will be conducted and findings reported after each wave of data collection.